T-Mobile is rolling out a new software update to the LG G3 which brings along with it a bunch of bug fixes among other things.
The update weighs around 132MB and is arriving with the build D85130g. It installs the monthly Google security patch (June) on the handset alongside fixing some bugs.
Speaking of which, the 2G/3G data roaming issue has now been resolved. LG app also receives a fix. Besides, the update contains a bunch of software and stability improvements.
Since the updates is small in size, you can download it over cellar data. But make sure you have a strong signal reception before hitting the download button.
Alternatively, you can download the update over a Wi-Fi network which will save you from unnecessary wastage of data as well.
The update has already been seeded over-the-air by T-Mobile, so it should hit your device anytime now. If you want to check for it manually, however, go to Settings > About phone > System updates.